U.S. patent application number 11/799876 was filed with the patent office on 2008-11-06 for making co-precipitated mixed oxide-treated titanium dioxide pigments.
This patent application is currently assigned to Tronox LLC. Invention is credited to Daniel H. Craig, Venkata Rama Rao Goparaju.
Application Number | 20080271642 11/799876 |
Document ID | / |
Family ID | 39577782 |
Filed Date | 2008-11-06 |
United States Patent
Application |
20080271642 |
Kind Code |
A1 |
Craig; Daniel H. ; et
al. |
November 6, 2008 |
Making co-precipitated mixed oxide-treated titanium dioxide
pigments
Abstract
Simplified and improved processes are provided for manufacturing
titanium dioxide pigments including a surface treatment whereby a
plurality of inorganic oxides or a combination of one or more
inorganic oxides with one or more inorganic phosphates are applied
to a titanium dioxide base pigment. Aqueous acid-soluble sources of
the desired inorganic oxides and/or phosphates are predissolved in
an aqueous acid, and these can be added on a batch wise or more
preferably on a continuous basis to an alkaline slurry containing
the titanium dioxide base pigment and to which aqueous
alkaline-soluble sources of the desired inorganic oxides are being
or have been added previously. Co-precipitation of the oxides
and/or oxides and phosphates is then accomplished by an adjustment
of the pH, to provide a surface treated pigment with excellent
homogeneity of the deposited mixed oxides and/or oxides and
phosphates.
Inventors: |
Craig; Daniel H.; (Edmond,
OK) ; Goparaju; Venkata Rama Rao; (Edmond,
OK) |
Correspondence
Address: |
William B. Miller;One Leadership Square
Suite 300, 211 North Robinson Avenue
Oklahoma City
OK
73102-7109
US
|
Assignee: |
Tronox LLC
|
Family ID: |
39577782 |
Appl. No.: |
11/799876 |
Filed: |
May 3, 2007 |
Current U.S.
Class: |
106/444 ;
106/449 |
Current CPC
Class: |
C09C 1/3661 20130101;
C01P 2004/62 20130101; C01P 2004/84 20130101 |
Class at
Publication: |
106/444 ;
106/449 |
International
Class: |
C09C 1/36 20060101
C09C001/36 |
Claims
1. A process for manufacturing a titanium dioxide pigment including
a surface treatment whereby a plurality of inorganic oxides or a
combination of one or more inorganic oxides with one or more
inorganic phosphates are applied to a titanium dioxide base pigment
from a chloride process or from a sulfate process, comprising the
steps of: a) preparing an aqueous alkaline slurry of titanium
dioxide base pigment from a sulfate or chloride process and in
which at least one aqueous alkali-soluble source of an inorganic
oxide has been dissolved; b) dissolving at least one aqueous
acid-soluble source of an inorganic oxide and/or at least one
aqueous acid-soluble salt of a cation capable of forming a
water-insoluble phosphate, into an aqueous sulfuric acid solution;
then c) gradually adding said sulfuric acid solution to the aqueous
alkaline slurry of titanium dioxide base pigment, the amount of
added sulfuric acid solution being sufficient to achieve a final
slurry pH value between about 4 up to about 8.5.
2. A process according to claim 1, wherein the titanium dioxide
base pigment selected has previously been surface treated to
deposit at least one inorganic oxide thereon from the group
consisting of the inorganic oxides of aluminum, boron, phosphorus,
silicon, titanium and zircomum.
3. A process according to claim 2, wherein the titanium dioxide
base pigment used to form the aqueous alkaline slurry includes from
about 0.5 percent to about 5 percent by weight of the inorganic
oxide or oxides, based on the weight of the treated pigment as a
whole.
4. A process according to claim 1, wherein the step a) is performed
by forming a mixture of titanium dioxide base pigment from a
sulfate or chloride process in water, and then adding to the
mixture at least one aqueous alkali-soluble oxide salt selected
from the group consisting of the aqueous alkali-soluble oxide salts
of aluminum, boron, phosphorus and silicon.
5. A process according to claim 4, wherein sodium or potassium
salts of aluminum, boron, phosphorus or silicon are used and added
in the form of an aqueous solution containing from about 1 percent
to about 50 percent by weight of the dissolved salts.
6. A process according to claim 5, wherein sodium or potassium
salts of aluminum, boron, phosphorus or silicon are used and added
in the form of an aqueous solution containing from about 5 percent
to about 40 percent by weight of the dissolved salts.
7. A process according to claim 6, wherein sodium or potassium
salts of aluminum, boron, phosphorus or silicon are used and added
in the form of an aqueous solution containing from about 15 percent
to about 35 percent by weight of the dissolved salts.
8. A process according to claim 1, wherein the at least one aqueous
acid-soluble source of an inorganic oxide or of a cation capable of
forming a water-insoluble phosphate is selected from the group
consisting of the aqueous acid-soluble salts of aluminum, cerium,
tin, titanium and zirconium.
9. A process according to claim 8, wherein the at least one aqueous
acid-soluble source of an inorganic oxide or of a cation capable of
forming a water-insoluble phosphate is added and dissolved into the
aqueous sulfuric acid solution in the form either of a previously
prepared aqueous metal salt solution or in solid salt form.
10. A process according to claim 1, wherein the aqueous sulfuric
acid solution used in step b) is from about 5 percent by weight up
to about 98 percent of sulfuric acid.
11. A process according to claim 10, wherein the aqueous sulfuric
acid solution used in step b) is from about 20 percent by weight up
to about 50 percent of sulfuric acid.
12. A process according to claim 11, wherein the aqueous sulfuric
acid solution used in step b) is from about 25 percent by weight up
to about 40 percent of sulfuric acid.
13. A process according to claim 1, wherein the titanium dioxide
base pigment is from about 5 percent up to about 65 percent by
weight of the aqueous alkaline slurry.
14. A process according to claim 13, wherein the titanium dioxide
base pigment is from about 15 percent to about 45 percent by weight
of the aqueous alkaline slurry.
15. A process according to claim 14, wherein the titanium dioxide
base pigment is from about 25 percent to about 40 percent by weight
of the aqueous alkaline slurry.
16. A process according to claim 1, wherein the plurality of
inorganic oxides or a combination of one or more inorganic oxides
with one or more inorganic phosphates that are deposited from the
alkali-soluble and acid-soluble sources collectively comprise from
about 0.2 percent to about 10 percent by weight of the pigment
based on titanium dioxide.
17. A process according to claim 16, wherein the plurality of
inorganic oxides or a combination of one or more inorganic oxides
with one or more inorganic phosphates that are deposited from the
alkali-soluble and acid-soluble sources collectively comprise from
about 0.5 percent to about 8 percent by weight of the pigment based
on titanium dioxide.
18. A process according to claim 17, wherein the plurality of
inorganic oxides or a combination of one or more inorganic oxides
with one or more inorganic phosphates that are deposited from the
alkali-soluble and acid-soluble sources collectively comprise from
about 1.0 percent to about 5 percent by weight of the pigment based
on titanium dioxide.
19. A process according to claim 16, wherein the weight ratio of
deposited oxide(s) and/or phosphate(s) from the alkali-soluble
sources to the acid soluble sources thereof is from about 30:1 to
about 1:10.
20. A process according to claim 19, wherein the weight ratio of
deposited oxide(s) and/or phosphate(s) from the alkali-soluble
sources to the acid soluble sources thereof is from about 20:1 to
about 1:1.
21. A process according to claim 20, wherein the weight ratio of
deposited oxide(s) and/or phosphate(s) from the alkali-soluble
sources to the acid soluble sources thereof is from about 15:1 to
about 2:1.
22. A process according to claim 1, further comprising depositing a
wet treatment aluminum oxide onto the titanium dioxide base
pigment, while maintaining a slurry pH between about 4 to about
8.5, after substantially completely co-precipitating the mixed
inorganic oxides and/or inorganic oxide and phosphate combination
onto the pigment according to step c).
23. A process for manufacturing a titanium dioxide pigment
including a surface treatment whereby a plurality of inorganic
oxides or a combination of one or more inorganic oxides with one or
more inorganic phosphates are applied to a titanium dioxide base
pigment from a chloride process or from a sulfate process,
comprising the steps of: a) dissolving at least one aqueous
acid-soluble source of an inorganic oxide and/or at least one
aqueous acid-soluble salt of a cation capable of forming a
water-insoluble phosphate, into an aqueous sulfuric acid solution;
b) dissolving at least one alkali-soluble source of an inorganic
oxide into an aqueous alkaline solution; then c) gradually adding
both said sulfuric acid solution and said aqueous alkaline solution
to an aqueous alkaline slurry of titanium dioxide base pigment from
a sulfate or chloride process, the amounts added of these solutions
being such as to achieve a final slurry pH value between about 4 up
to about 8.5.
Description
FIELD OF THE INVENTION
[0001] This invention relates to processes for making titanium
dioxide pigments including a co-precipitated mixed inorganic oxide
or mixed oxide/phosphate surface treatment. The resulting pigments
are useful in many industries including the coatings, paper, and
plastics industries.
BACKGROUND OF THE INVENTION
[0002] Titanium dioxide is used as an opacifier and colorant in
many industries, including the coatings, plastics, and paper
industries. In general, the effectiveness of the pigment in such
applications depends on how evenly the pigment can be dispersed in
a coating, in plastic or in paper. For this reason, pigments are
generally handled in the form of a finely divided powder. However,
titanium dioxide powders are inherently dusty and frequently
exhibit poor powder flow characteristics, especially during
formulation, compounding, and manufacture of end-use products.
While free-flowing powders with low dust properties can be obtained
through known manufacturing practices, these powders usually
exhibit reduced opacifying properties.
[0003] To this end, chemical methods of modification of titanium
dioxide pigment surfaces have been developed to achieve the desired
balance of pigment opacity and flow characteristics. For instance,
it is known in the art that the wetting and dispersing properties
of titanium dioxide pigments can be improved by exposure of a
titanium dioxide intermediate (produced by either a sulfate or
chloride process) to certain inorganic treatments through the
deposition of inorganic metal oxide and/or metal hydroxide coatings
on the surface of the titanium dioxide. Typically these treatments
are accomplished by:
[0004] (1) dispersing the intermediate (or crude) material in an
aqueous medium using a dispersing agent such as a
polyphosphate,
[0005] (2) optionally wet milling the resulting slurry to achieve a
certain desired particle size,
[0006] (3) precipitating one or more inorganic oxides such as
silica or alumina onto the particle surfaces of the titanium
dioxide slurry,
[0007] (4) recovering the inorganic oxide treated titanium dioxide
pigment from the aqueous slurry by filtration,
[0008] (5) washing the filtered product to remove salts and
impurities,
[0009] (6) drying the washed filtered product, and
[0010] (7) dry-milling the dried pigment using a fluid energy
mill.
[0011] Typically the wet treatment deposition of inorganic oxides
according to step (3) is accomplished - for pigments treated with
more than one inorganic oxide - in a sequential fashion, one
inorganic oxide at a time. However, it is also known to chemically
treat titanium dioxide pigment intermediates with co-precipitated
mixed inorganic oxides. Apart from reducing the total number of
inorganic surface treatments to be performed, titanium dioxide
pigments bearing co-precipitated mixed inorganic oxide treatments
perform differently as compared to pigments wherein the same
inorganic oxides are added sequentially.
[0012] A number of references describe or at least suggest titanium
dioxide pigments including a co-precipitated, mixed inorganic oxide
surface treatment. For example, U.S. Pat. No. 2,913,419 discloses a
broad range of particles, including titanium dioxide particles,
surface treated with dense silica-containing codeposited silicates
and/or metal oxides selected from the group of silicates and oxides
of metals which form insoluble silicates at a pH between five and
twelve, including silicates and oxides of aluminum, tin, titanium,
zinc, and zirconium.
[0013] U.S. Pat. No. 3,513,007 claims an improved process for
coating titanium dioxide pigment particles comprising the treatment
of titanium dioxide pigment particles in an aqueous medium, in two
sequential steps, with first at least one compound selected from
the group consisting of water-soluble hydrolysable compounds of
silicon, titanium, zirconium, and phosphates, and secondly with at
least one water-soluble hydrolysable compound of aluminum, cerium,
calcium, or mixtures thereof, while maintaining the pH of the
suspension in the range of six to ten. The pigments produced
according to the process of the invention are said to exhibit
higher tinting strength and gloss when incorporated into
paints.
[0014] Great Britain Patent 1,256,421 describes an improved process
for treating metal oxide particles which have already been treated
with a coating of one or more oxides or hydrous oxides of titanium,
aluminum, cerium, silicon, zinc, zirconium, or a phosphate, with an
alkaline aqueous solution of hydrolysable aluminum salt to provide
a second alumina coating. Specific examples of the initial mixed
oxide coatings comprise titania/alumina or zirconia/alumina. Such
treatments are said to result in improved pigment durability and
gloss properties.
[0015] U.S. Pat. No. 3,649,322 discloses an aluminum
silicate-encapsulated pigmentary titanium dioxide, combining high
tinting strength and durability in coating compositions, which is
prepared by co-precipitating hydrous silicon oxide with hydrous
aluminum oxide onto titanium dioxide in aqueous slurry, to form a
dense coating of aluminum silicate. When the dense aluminum
silicate coating is applied in a single stage, the pigment is
further treated with an additional coating of aluminum oxide.
[0016] U.S. Pat. No. 3,825,438 claims a process for coating
titanium dioxide pigments with at least one hydrous oxide of a
metal, comprising mixing an aqueous dispersion of titanium dioxide
pigment with at least one water-soluble hydrolysable compound of a
metal selected from the group consisting of aluminum, titanium,
cerium, zirconium, silicon and zinc, then adding to the dispersion
a polyhydric alcohol containing at least two hydroxy groups and
from two to eight carbon atoms, and finally precipitating a hydrous
oxide of the metal onto the surface of the particles of titanium
dioxide by effecting a change in the pH of the dispersion. The
examples teach co-precipitated treatments derived from mixed
solutions of titanyl sulfate and aluminum sulfate. The pigments
produced by the process of the invention can be used in a wide
variety of products, including paints, plastics, and paper.
[0017] U.S. Pat. No. 4,052,224 discusses a process for treating a
titanium dioxide pigment, using first a mixed solution of
water-soluble compounds of aluminum, zirconium, and titanium, and
then providing a final inorganic surface treatment with an aluminum
phosphate. The resulting pigments are described as particularly
useful in the manufacture of paints having reduced photochemical
activity, and in the manufacture of paper laminates.
[0018] U.S. Pat. No. 4,115,144 describes the co-precipitation of
metal oxides (such as, for example, alumina and titania) onto a
titanium dioxide pigment, through dissolving water-soluble
compounds that will precipitate as or be convertible to the desired
mixed metal oxide form in water, and then adding this solution to
an aqueous dispersion of titanium dioxide and precipitating the
metal oxides under alkaline conditions as through the addition of
sodium hydroxide. After filtration and washing, the coated and
washed titanium dioxide is hot aged in the presence of water under
alkaline conditions, the hot ageing step being described as
necessary to avoid processing difficulties and give "suitable
charge and pH characteristics".
[0019] U.S. Pat. No. 4,328,040 describes a process for the
production of titanium dioxide pigments with "improved chalking
resistance and gloss retention", wherein oxides and/or phosphates
of titanium, zirconium, aluminum and silicon are applied to
titanium dioxide, by adding alkaline zirconium carbonate complexes
of the alkali metals or ammonium to an aqueous alkaline pigment
suspension, and then adding a solution of dissolved compounds of
titanium and/or aluminum and/or silicon and/or phosphorus to slowly
precipitate the oxides and/or phosphates onto the pigment.
[0020] U.S. Pat. No. 4,405,376 provides a titanium dioxide pigment
and a process for making the same, wherein the pigment comprises a
pigmentary titanium dioxide core particle, a mixed inner coating of
hydrous oxides of tin and zirconium, and an outer coating of a
hydrous oxide of aluminum.
[0021] U.S. Pat. No. 4,450,012 discloses coated rutile mixed phase
pigments having a first coating of an oxide or mixture of oxides of
titanium, zirconium, or tin, and a subsequent coating of an oxide
of aluminum. The resulting pigments exhibit an improved tendency
against flocculation in lacquers hardened with acid catalysts.
[0022] U.S. Pat. No. 4,759,800 describes a process for chemically
treating titanium dioxide pigment wherein titania is deposited
first from a solution of titanium oxychloride, and then an alumina
outer treatment is performed. Many examples illustrate the
co-deposition, or co-precipitation, of other metal oxides along
with the deposited titania, including titania/alumina,
titania/zirconia, and zirconia/titanialsilica co-precipitated
combinations. The resulting pigments purportedly exhibit improved
weathering resistance and optical properties.
[0023] U.S. Pat. No. 4,781,761 discloses that co-deposition of
boria with silica, preferably from a master solution containing
water-soluble sodium silicate and sodium borate, enables the
formation of dense silicate coatings on titanium dioxide particles
at lower processing temperatures than used previously to achieve
dense silica coatings. The resulting boria-modified
silica-containing pigments are highly lightfast, and exhibit
excellent gloss and dispersibility.
[0024] U.S. Pat. No. 5,753,025 discloses a process for making a
rutile titanium dioxide pigment suitable for use in making coatings
having improved gloss, through co-deposition of boric with silica,
followed by treatment with an oxide of aluminum.
[0025] U.S. Pat. No. 7,135,065 describes the production of titanium
dioxide pigments in which aqueous solutions of water-soluble
compounds of tin and zirconium as well as at least one more of
aluminum, silicon and titanium are added to an aqueous suspension
of titanium dioxide base material maintained at a pH of not more
than 3 or less than 10, and then the pH value of the suspension is
adjusted to between 6 and 8 to cause the corresponding oxides to be
deposited on the titanium dioxide base material.
[0026] U. S. Patent Application Publication 20040025749 A1
discloses a method for preparation of titanium dioxide pigment
exhibiting high greying resistance and high hiding power, in which
the pH value of a suspension of titanium dioxide material, a
phosphorus compound, a titanium compound and an aluminum compound
is adjusted to about 9, followed by the addition of a magnesium
compound while maintaining the pH value above about 8.5.
[0027] U.S. Patent Application Publication 20050011408 A1 describes
a method for the surface treatment of a titanium dioxide pigment,
comprising the steps of: a) adding an aluminum component and a
phosphorus component to a titanium dioxide suspension while the pH
value of the suspension is maintained at a value greater than or
equal to ten; and then b) adding an acid component to the
suspension until the pH value is less than nine. It is also taught
that together with the aluminum component and the phosphorus
component, other metal salt solutions, such as salts of cerium,
titanium, silicon, zirconium, or zinc, can also be added to the
suspension in step a), these subsequently being jointly
precipitated onto the particle surface in step b) as phosphate or
hydrated oxide.
[0028] U.S. Patent Application Publication 20060032402 A1 relates
to titanium dioxide pigment particles having two or more layers
deposited thereon, wherein at least one of the two or more layers
is a dense silicon dioxide layer comprising silicon dioxide
containing no significant quantity of metal atoms other than
silicon, and wherein at least one of the two or more layers is a
dense silicon dioxide layer containing a significant quantity of
co-precipitated oxides of metal ions or mixtures of metal ions
other than silicon. The resulting pigments are weather resistant
and particularly suitable for use in surface coatings and
plastics.
[0029] U.S. Patent Application Publication 20060034739 A1 relates
to a method for treatment of titanium dioxide characterized in
that, together with the hydrous oxides of tin and zirconium, at
least one other from the group consisting of aluminum, silicon, and
titanium is additionally co-precipitated onto the particle surface.
The treated pigment is subsequently treated with an oxide of
aluminum. Compared with the prior art, the resulting pigments
demonstrate a further improvement in photostability, while
retaining good optical properties and are particularly suitable for
use in paints, coatings, and plastics.
[0030] Despite the many titanium dioxide pigments thus described as
having mixed inorganic oxides applied via co-precipitation or
co-deposition, however, none of the aforementioned references
anticipate or suggest the process efficiencies enabled by the
present invention and described in greater detail below, nor the
product consistency and uniformity of co-precipitant incorporation
improvements realized through the present invention.
SUMMARY OF THE PRESENT INVENTION
[0031] The present invention concerns simplified and improved
processes for manufacturing titanium dioxide pigments including a
surface treatment whereby a plurality of inorganic oxides or a
combination of one or more inorganic oxides with one or more
inorganic phosphates are applied to a titanium dioxide base
pigment.
[0032] In a first embodiment, a process according to the present
invention comprises the steps of a) preparing an aqueous alkaline
slurry of titanium dioxide base pigment from a sulfate or chloride
process and in which at least one aqueous alkali-soluble source of
an inorganic oxide has been dissolved, b) dissolving at least one
aqueous acid-soluble source of an inorganic oxide and/or at least
one aqueous acid-soluble salt of a cation capable of forming a
water-insoluble phosphate, into an aqueous sulfuric acid solution,
then c) gradually adding said sulfuric acid solution to the aqueous
alkaline slurry of titanium dioxide base pigment, the amount of
added sulfuric acid solution being sufficient to achieve a final
slurry pH value between about 4 up to about 8.5.
[0033] In a second embodiment, a process according to the present
invention comprises the steps of a) dissolving at least one aqueous
acid-soluble source of an inorganic oxide and/or at least one
aqueous acid-soluble salt of a cation capable of forming a
water-insoluble phosphate, into an aqueous sulfuric acid solution,
b) dissolving at least one alkali-soluble source of an inorganic
oxide into an aqueous alkaline solution, c) then gradually adding
both said sulfuric acid solution and said aqueous alkaline solution
to an aqueous alkaline slurry of titanium dioxide base pigment from
a sulfate or chloride process, the amounts added of these solutions
being such as to achieve a final slurry pH value between about 4 up
to about 8.5.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE PRESENT
INVENTION
[0034] In the first embodiment, an improved process is provided for
the co-precipitation of mixed inorganic oxides or oxide/phosphate
combinations onto a titanium dioxide base pigment, which process
preferably comprises the following steps:
[0035] (a) forming a mixture comprising titanium dioxide base
pigment in water, said titanium dioxide base pigment having been
produced by either a sulfate process or a vapor phase
oxidation-based chloride process and wherein, optionally, at least
one wet treatment inorganic oxide selected from the group
consisting of the inorganic oxides of aluminum, boron, phosphorus,
silicon, titanium and zirconium has been deposited on said titanium
dioxide base pigment;
[0036] (b) adding to the slurry from step (a) at least one aqueous
alkali-soluble oxide salt selected from the group consisting of the
aqueous alkali-soluble oxide salts of aluminum, boron, phosphorus
and silicon;
[0037] (c) dissolving i) at least one aqueous acid-soluble salt
selected from the group consisting of the aqueous acid-soluble
salts of aluminum, cerium, tin, titanium and zirconium and/or ii)
at least one aqueous acid-soluble salt of a cation capable of
forming a water-insoluble phosphate, into an aqueous sulfuric acid
solution;
[0038] (d) gradually adding to the slurry prepared in step (b) said
solution prepared in step (c), in an amount sufficient to achieve a
final slurry pH value from about 4 to about 8.5, so as to
facilitate a complete, uniform and consistent co-precipitation of
the mixed inorganic oxides and/or inorganic oxide(s) and
phosphate(s); and
[0039] (e) after step (d), optionally depositing a wet treatment
aluminum oxide onto the titanium dioxide particles in the slurry
prepared in step (d), while maintaining said slurry pH between
about 4 to about 8.5.
[0040] In the second embodiment, a process for the co-precipitation
of mixed inorganic oxides onto titanium dioxide base pigment
preferably comprises:
[0041] (a) forming a mixture comprising titanium dioxide base
pigment in water, said titanium dioxide base pigment having been
produced by either a sulfate process or a vapor phase
oxidation-based chloride process and wherein, optionally at least
one wet treatment inorganic oxide selected from the group
consisting of the inorganic oxides of aluminum, boron, phosphorus,
silicon, titanium and zirconium has been deposited on said titanium
dioxide base pigment;
[0042] (b) forming an aqueous solution of at least one aqueous
alkali-soluble oxide salt selected from the group consisting of the
aqueous alkali-soluble oxide salts of aluminum, boron, phosphorus
and silicon;
[0043] (c) dissolving into an aqueous sulfuric acid solution i) at
least one aqueous acid-soluble salt selected from the group
consisting of the aqueous acid-soluble salts of aluminum, cerium,
tin, titanium and zirconium and/or ii) at least one other aqueous
acid-soluble salt selected from the group consisting of the aqueous
acid-soluble salts of aluminum, cerium, magnesium, titanium, zinc
and zirconium;
[0044] (d) gradually adding to the slurry resulting from step (a),
in two separate process streams, said solutions prepared in steps
(b) and (c), in amounts sufficient to achieve a final slurry pH
value in the range of from about 4 to about 8.5, so as to
facilitate a complete, uniform and consistent co-precipitation of
the mixed inorganic oxide(s) and/or oxide(s) and phosphate(s);
and
[0045] (e), after step (d), optionally depositing a wet treatment
aluminum oxide, while maintaining said slurry pH between a value of
about 4 to about 8.5.
[0046] The resulting treated titanium dioxide pigment particles are
typically further processed through several additional
manufacturing steps as elaborated below, including filtration,
washing, drying, and fluid energy milling, in the presence or
absence of additional known functional additives, to yield a
finished pigment suitable for use in coatings, paper, plastics, and
cosmetics.
[0047] Dissolving the aqueous acid-soluble source of inorganic
oxide and/or water-insoluble phosphate into the aqueous sulfuric
acid solution in the manner of the instant invention, prior to the
adjustment of the slurry pH value with the sulfuric acid solution,
provides a simplified process to achieve co-precipitated oxide
and/or phosphate treatments in that fewer required reagent addition
streams are used. Further, while co-precipitation of inorganic
oxides as carried out in U.S. Pat. Nos. 4,115,144, 4,328,040 and
7,135,065, for example, is on a batch wise basis, the process of
the present invention can in either embodiment be carried out on
either a batch wise basis or more preferably on a continuous basis.
Those skilled in the art will readily appreciate that for materials
produced on a very large scale, as titanium dioxide pigments are,
the ability to carry out a surface treatment process on a
continuous basis offers very significant benefits and
advantages.
[0048] In addition, greater product consistency is also achieved as
compared to mixed oxide-treated pigments produced by the prior
methods. While not wishing to be held to any one theory, it is
speculated that the intimate molecular-level mixing that occurs
through dissolving the acid-soluble source of inorganic oxide into
the same sulfuric acid reagent as used to precipitate out the
alkali-soluble inorganic oxide enables more uniform inorganic oxide
and/or phosphate co-precipitation, correspondingly also allowing
for increased control over and greater uniformity of the mixed
oxide and/or phosphate stoichiometries during the co-precipitation
process, as compared to processes of the prior art. Thus the
process of the instant invention enables greater "fine-tuning" of
pigment end-use properties.
[0049] In general, any type of titanium dioxide material can be
processed in accordance with the instant invention. Preferred is
rutile titanium dioxide base pigment produced from either the
sulfate or chloride process. Most preferred is rutile titanium
dioxide which has been produced via the chloride process from
titanium tetrachloride using a vapor phase oxidation step. The
titanium dioxide material can also contain an amount of alumina,
from aluminum chloride which has been conventionally added as a
rutilization aid during the vapor phase oxidation step along with
the titanium tetrachloride. Other inorganic oxides formed during
the oxidation step may be present as well, to the extent one
skilled in the art may wish to incorporate other oxidizable
inorganic materials in the oxidation step as has been described or
suggested elsewhere for various purposes, for example, particle
size control; see, for instance, U.S. Pat. Nos. 3,856,929,
5,201,949, 5,922,120 and 6,562,314.
[0050] The aqueous slurry of titanium dioxide base pigment can be
usefully employed at concentrations from about 5% by weight of
titanium dioxide up to about 65% by weight of titanium dioxide.
Preferred are concentrations from about 15% by weight of titanium
dioxide up to about 45% by weight. Most preferred are
concentrations from about 25% by weight of titanium dioxide up to
about 40% by weight.
[0051] Pertaining to step (a) in both aspects of the present
invention, the optional wet treatment inorganic oxide can be
applied utilizing any of the known processes to effect deposition
of inorganic oxides onto the titanium dioxide. The number of
treatments, and the manner of their application, are not critical,
and various possibilities are well known to those skilled in the
art, so further detail on this aspect is not necessary.
Nevertheless, by way of example of known inorganic oxide treatment
protocols, for plastics end-use applications U.S. Pat. Nos.
5,332,433 and 5,700,318 describe inorganic treatment protocols, as
do U.S. Pat. Nos. 5,203,916 and 5,976,237 for coatings end-use
applications. Typically, the optional wet treatment oxide when
//deposited, is present in an amount from about 0.5% up to about 5%
by weight calculated on treated pigment.
[0052] The alkali-soluble source of inorganic oxide can be added to
the aqueous slurry of titanium dioxide particles as an aqueous
oxide salt solution, said solution containing from about 1% by
weight up to about 50% by weight of dissolved alkali-soluble salt.
Preferred are aqueous solutions containing from about 5% by weight
up to about 40% by weight of dissolved alkali-soluble salt. Most
preferred are aqueous solutions containing from about 15% by weight
up to about 35% by weight of dissolved alkali-soluble salt.
Preferred are sodium and potassium salts, or mixtures thereof.
[0053] The aqueous sulfuric acid solution comprises sulfuric acid
in an amount from about 5% by weight up to about 98% by weight of
the solution, but preferably is from about 20% by weight up to
about 50% by weight of dissolved sulfuric acid and most preferably
comprises from about 25% by weight up to about 40% by weight of
dissolved sulfuric acid.
[0054] The acid-soluble source of inorganic oxide and/or
acid-soluble salt of a cation capable of forming a water-insoluble
phosphate can be dissolved into the aqueous sulfuric acid solution
from a previously prepared aqueous metal salt solution or from a
solid salt, said sulfuric acid solution ultimately containing
dissolved acid-soluble salts in amounts calculated to achieve from
about 0.05% up to about 8% of co-precipitated oxide and/or
phosphate, by weight based on titanium dioxide. Preferred is
dissolved acid-soluble salt in an amount calculated to achieve from
about 0.1% up to about 5% of co-precipitated oxide and/or
phosphate, by weight based on titanium dioxide. Most preferred is
dissolved acid-soluble salt in an amount calculated to achieve from
about 0.2% up to about 2.0% of co-precipitated oxide and/or
phosphate, by weight based on titanium dioxide. The acetate,
chloride, nitrate, and sulfate metal salts are preferred.
[0055] Typically, the wet treatment mixed inorganic oxides and/or
phosphates are deposited according to the process of the instant
invention in amounts as an additive sum from about 0.2% up to about
10% by weight calculated on treated pigment, preferably from about
0.5% up to about 8% by weight calculated on treated pigment, most
preferably from about 1.0% up to about 5% by weight calculated on
treated pigment, wherein the weight ratio of the deposited oxide
and/or phosphate from the alkali-soluble source of an inorganic
oxide and/or phosphate to the deposited oxide and/or phosphate from
the acid-soluble source of an inorganic oxide and/or phosphate is
between about 30:1 to about 1:10. Preferred is a ratio between
about 20:1 to about 1:1. Most preferred is a ratio between about
15:1 to about 2:1.
[0056] Pertaining to step (e) in both aspects of the present
invention, the optional wet treatment aluminum oxide can be applied
utilizing any of the known processes for depositing aluminum oxides
onto the titanium dioxide. Typically, when present, the wet
treatment aluminum oxide is present in an amount from about 0.5% up
to about 5% by weight calculated on treated pigment. The optional
wet treatment aluminum oxide can also have optionally co-deposited
therein co-precipitated oxides and/or phosphates without departing
from the spirit and scope of the invention.
[0057] Further processing of the wet-treated titanium dioxide
pigment particles can be accomplished by filtration using a
vacuum-type filtration system or a pressure-type filtration system,
washing, and drying, using any of the procedures known in the art.
For drying, this would include vacuum drying, spin-flash drying, or
spray drying to produce a dry titanium dioxide pigment powder. The
preferred method is spray drying. The dry product thus produced can
be optionally ground to a desired final particle size distribution
using, for example, conventional steam micronization in the
presence or absence of additional functional additives as known in
the art.
[0058] The following examples serve to illustrate specific
embodiments of the instant invention, without intending to limit or
restrict the scope of the invention as disclosed herein.
Concentrations and percentages are by weight unless otherwise
indicated.
ILLUSTRATIVE EXAMPLES
Example 1
[0059] Particulate titanium dioxide pigment intermediate obtained
from the vapor phase oxidation of titanium tetrachloride containing
1.0% alumina was dispersed in water in the presence of 0.15% by
weight (based on pigment) of sodium hexametaphosphate dispersant,
along with a sufficient amount of sodium hydroxide to adjust the pH
of the dispersion to a value of 9.5 or greater, to achieve an
aqueous dispersion with a solids content of 35% by weight. The
resulting titanium dioxide slurry was sand milled, using a zircon
sand-to-pigment weight ratio of 4 to 1, until a volume average
particle size was achieved wherein more than 90% of the particles
were smaller than 0.63 microns, as determined utilizing a Microtrac
X100 Particle Size Analyzer (Microtrac Inc. Montgomeryville,
Pa.).
[0060] The resulting slurry, diluted to 30% solids by weight, was
heated to 90.degree. C. and subsequently treated with 3.0%,
calculated as silica by weight of final pigment, of sodium
silicate, added over 20 minutes as a 250 gram/liter aqueous sodium
silicate solution. While maintaining the temperature at 90.degree.
C., the pH of the slurry was slowly decreased to a pH of 5.0 over a
55 minute period via the slow addition of 36% by weight aqueous
sulfuric acid solution, said sulfuric acid solution containing
zirconium oxychloride dissolved therein at a concentration
calculated to achieve 0.2%, by weight based on titanium dioxide, of
co-precipitated zirconium oxide. Following a digestion period of 15
minutes at a pH of 5, 2.0% alumina, by weight of final pigment, was
added over 20 minutes as a 180 gram/liter aqueous sodium aluminate
solution, while maintaining the pH of the slurry between a value of
8.0 and 8.5 via the concomitant addition of 36% aqueous sulfuric
acid solution, said sulfuric acid solution containing no other
dissolved ingredients.
[0061] The dispersion was allowed to equilibrate at 90.degree. C.
for 15 minutes, at which point the pH of the slurry was re-adjusted
to 5.8, prior to filtration while hot. The resulting filter cake
was washed with an amount of water, which had been preheated to
60.degree. C. and pre-adjusted to a pH of 7.0, equal to 1.5 times
the estimated weight of recovered pigment.
[0062] The washed semi-solid filter cake was subsequently
re-dispersed in water with agitation, and dried using an APV Nordic
PSD52 Spray Dryer (Invensys APV Silkeborg, Denmark), maintaining a
dryer inlet temperature of approximately 280.degree. C., to yield a
dry pigment powder. The dry pigment powder was then steam
micronized in the presence of 0.35% by weight based on pigment of
trimethylol propane, utilizing a steam to pigment weight ratio of
2.5, with a steam injector pressure set at 146 psi and micronizer
ring pressure set at 118 psi, completing the finished pigment
preparation.
[0063] The zirconia content of the resulting pigment produced
according to the inventive process was determined via known X-ray
fluorescence techniques utilizing a PANalytical PW2404 Spectrometer
(PANalytical B. V. Almelo, The Netherlands), with appropriate
calibration to standards and matrix corrections.
[0064] To help determine the degree of effectiveness and uniformity
of incorporation of the co-precipitated zirconia according to the
process of the instant invention, pigment photocatalytic activity
was determined utilizing the technique documented in T. I.
Brownbridge and J. R. Brand, "Photocatalytic Activity of Titanium
Dioxide Pigment", Surface Coatings Australia, September 1990, pages
6-11 (paper presented at the 32nd Annual SCAA Convention, Perth,
Wash., September 1990), as referenced and further described in U.S.
Pat. No. 5,730,796. This involves the steps of: (1) placing about
0.2 g of the TiO.sub.2 product in about 40 ml of
spectroscopic-grade isopropanol; (2) exposing the
TiO.sub.2/isopropanol composition to ultra-violet light; (3)
monitoring the formation of acetone in the test composition over
time; (4) determining, by linear regression analysis, a linear rate
of acetone formation in the test composition; and (5) multiplying
the calculated rate value by a factor of 1000. The resulting value
(reported as High Sensitivity Photocatalytic Activity (HSPCA)
slope) is proportional to the photocatalytic response of the
pigment upon exposure to ultraviolet light, and provides a measure
of accelerated weathering performance of coatings or plastics
incorporating the pigment product. Smaller values indicate greater
suppression of inherent titanium dioxide pigment photocatalytic
activity, and therefore greater durability, or greater resistance
to discoloration, both of which directly result from more efficient
and uniform incorporation of co-precipitated zirconium oxides into
the silica surface treatment.
[0065] Results are provided in Table 1, together with comparative
results from two finished pigment samples; the first prepared
utilizing the same procedure described above, except that the
zirconium oxychloride reagent was batch-added at the beginning of
the silica deposition step (Comparative Example 1A), and the second
prepared utilizing the same procedure described above, but in the
absence of the addition of zirconium oxychloride to the sulfuric
acid solution used during the silica deposition step, thus
replacing the mixed oxide treatment of co-precipitated silica and
zirconia with 3% deposited silica (Comparative Example 1B).
TABLE-US-00001 TABLE 1 Pigment Zirconia Content and Photocatalytic
Activity Value Co-precipitated HSPCA Pigment Sample Zirconia
content (wt. %) slope Example 1 0.20 1.0 Comparative Example 1A
0.20 2.3 Comparative Example 1B none 2.5
[0066] Example 1 illustrates the novel process of the instant
invention, wherein titanium dioxide pigment is produced having
deposited thereon in two sequential steps, a mixed inorganic oxide
wet treatment comprising 3.0% dense silica co-precipitated with
0.2% zirconia, followed by 2.0% alumina (percents are by weight of
the pigment). The substantial durability performance increase
(decreased HSPCA value versus comparative example) of the inventive
pigment indicates uniform incorporation of the co-precipitated
zirconia into the silica treatment. The resulting titanium dioxide
pigment is particularly useful in the production of end-use
articles and compositions including plastics and coatings,
especially for exterior applications.
Example 2
[0067] Particulate titanium dioxide pigment intermediate obtained
from the vapor phase oxidation of titanium tetrachloride containing
1.0% alumina was dispersed in water in the presence of 0.15% by
weight (based on pigment) of sodium hexametaphosphate dispersant,
along with a sufficient amount of sodium hydroxide to adjust the pH
of the dispersion to a value of 9.5 or greater, to achieve an
aqueous dispersion with a solids content of 35% by weight. The
resulting titanium dioxide slurry was sand milled, using a zircon
sand-to-pigment weight ratio of 4 to 1, until a volume average
particle size was achieved wherein more than 90% of the particles
were smaller than 0.63 microns, as determined utilizing a Microtrac
X100 Particle Size Analyzer.
[0068] The resulting slurry, diluted to 30% solids by weight, was
heated to 90.degree. C. and subsequently treated with 3.0%,
calculated as silica by weight of final pigment, of sodium
silicate, added over 20 minutes as a 250 gram/liter aqueous sodium
silicate solution. While maintaining the temperature at 90.degree.
C., the pH of the slurry was slowly decreased to a pH of 5.0 over a
55 minute period via the slow addition of 36% by weight aqueous
sulfuric acid solution, said sulfuric acid solution containing
aluminum sulfate dissolved therein at a concentration calculated to
achieve 0.5%, by weight based on titanium dioxide, of
co-precipitated aluminum oxide. Following a digestion period of 15
minutes at pH=5, 2.0% alumina, by weight of final pigment, was
added over 20 minutes as a 180 gram/liter aqueous sodium aluminate
solution, while maintaining the pH of the slurry between a value of
8.0 and 8.5 via the concomitant addition of 36% aqueous sulfuric
acid solution, said sulfuric acid solution containing no other
dissolved ingredients.
[0069] The dispersion was allowed to equilibrate at 90.degree. C.
for 15 minutes, at which point the pH of the slurry was re-adjusted
to 5.8, prior to filtration while hot. The resulting filter cake
was washed with an amount of water, which had been preheated to
60.degree. C. and pre-adjusted to a pH of 7.0, equal to 1.5 times
the estimated weight of recovered pigment.
[0070] The washed semi-solid filter cake was subsequently
re-dispersed in water with agitation, and dried using an APV Nordic
PSD52 Spray Dryer, maintaining a dryer inlet temperature of
approximately 280.degree. C., to yield a dry pigment powder. The
dry pigment powder was then steam micronized in the presence of
0.35% by weight based on pigment of trimethylol propane, utilizing
a steam to pigment weight ratio of 2.5, with a steam injector
pressure set at 146 psi and micronizer ring pressure set at 118
psi, completing the finished pigment preparation.
[0071] The alumina content of the resulting pigment produced
according to the inventive process was determined via known X-ray
fluorescence techniques utilizing a PANalytical PW2404
Spectrometer, with appropriate calibration to standards and matrix
corrections.
[0072] To determine the degree of effectiveness and uniformity of
incorporation of the co-precipitated alumina according to the
process of the instant invention, pigment photocatalytic activity
was determined as described in Example 1. Smaller values indicate
greater suppression of inherent titanium dioxide pigment
photocatalytic activity, and therefore greater durability, or
greater resistance to discoloration, both of which directly result
from more efficient and uniform incorporation of co-precipitated
aluminum oxides into the silica surface treatment.
[0073] Results are provided in Table 2, together with comparative
results from two finished pigment samples; the first prepared
utilizing the same procedure described above, except that the
aluminum sulfate reagent was batch-added at the beginning of the
silica deposition step (Comparative Example 2A), and the second
prepared utilizing the same procedure described above, but in the
absence of the addition of aluminum sulfate to the sulfuric acid
solution used during the silica deposition step, thus replacing the
mixed oxide treatment of co-precipitated silica and alumina with 3%
deposited silica (Comparative Example 2B).
TABLE-US-00002 TABLE 2 Pigment Zirconia Content and Photocatalytic
Activity Value Total Alumina Pigment Sample content (wt. %) HSPCA
slope Example 2 3.5 1.2 Comparative Example 2A 3.5 2.0 Comparative
Example 2B 3.0 2.5
[0074] Example 2 illustrates the novel process of the instant
invention, wherein titanium dioxide pigment is produced having
deposited thereon in two sequential steps, a mixed inorganic oxide
wet treatment comprising co-deposited 3.0% dense silica and 0.5%
alumina, followed by 2.0% alumina (percents are by weight of the
pigment). The substantial durability performance increase
(decreased HSPCA value versus comparative example) of the inventive
pigment indicates uniform incorporation of the co-precipitated
alumina into the silica treatment. The resulting titanium dioxide
pigment is particularly useful in the production of end-use
articles and compositions including plastics and coatings,
especially for exterior applications.
Example 3
[0075] Particulate titanium dioxide pigment intermediate obtained
from the vapor phase oxidation of titanium tetrachloride containing
1.0% alumina was dispersed in water in the presence of 0.15% by
weight (based on pigment) of sodium hexametaphosphate dispersant,
along with a sufficient amount of sodium hydroxide to adjust the pH
of the dispersion to a value of 9.5 or greater, to achieve an
aqueous dispersion with a solids content of 35% by weight. The
resulting titanium dioxide slurry was sand milled, using a zircon
sand-to-pigment weight ratio of 4 to 1, until a volume average
particle size was achieved wherein more than 90% of the particles
were smaller than 0.63 microns, as determined utilizing a Microtrac
X100 Particle Size Analyzer.
[0076] The resulting slurry, diluted to 30% solids by weight, was
heated to 90.degree. C. and subsequently treated with 3.0%,
calculated as silica by weight of final pigment, of sodium
silicate, added over 30 minutes as a 250 gram/liter aqueous sodium
silicate solution in parallel with the addition of 36% by weight
sulfuric acid solution to lower the slurry pH to 5, while
maintaining the temperature at 90.degree. C. Following a digestion
period of 15 minutes at a pH of 5, 2.0% alumina, by weight of final
pigment, was added over 20 minutes as a 180 gram/liter aqueous
sodium aluminate solution, while maintaining the pH of the slurry
at a value of 7.0 via the concomitant addition of 36% aqueous
sulfuric acid solution, said sulfuric acid solution containing
zirconium oxychloride dissolved therein at a concentration
calculated to achieve 0.2%, by weight based on titanium dioxide, of
co-precipitated zirconium oxide.
[0077] The dispersion was allowed to equilibrate at 90.degree. C.
for 15 minutes, at which point the pH of the slurry was re-adjusted
to 5.8, prior to filtration while hot. The resulting filter cake
was washed with an amount of water, which had been preheated to
60.degree. C. and pre-adjusted to a pH of 7.0, equal to 1.5 times
the estimated weight of recovered pigment.
[0078] The washed semi-solid filter cake was subsequently
re-dispersed in water with agitation, and dried using an APV Nordic
PSD52 Spray Dryer, maintaining a dryer inlet temperature of
approximately 280.degree. C., to yield a dry pigment powder. The
dry pigment powder was then steam micronized in the presence of
0.35% by weight based on pigment of trimethylol propane, utilizing
a steam to pigment weight ratio of 2.5, with a steam injector
pressure set at 146 psi and micronizer ring pressure set at 118
psi, completing the finished pigment preparation.
[0079] The resulting pigment produced according to the inventive
process was tested for zirconia content and photocatalytic activity
as described in Example 1. Results are provided in Table 3,
together with comparative results from two finished pigment
samples; the first prepared utilizing the same procedure described
above, except that the zirconium oxychloride reagent was
batch-added immediately before the addition of the sodium aluminate
solution (Comparative Example 3A), and the second prepared
utilizing the same procedure described above, but in the absence of
the addition of zirconium oxychloride to the sulfuric acid solution
used during the alumina deposition step, thus replacing the mixed
oxide treatment of co-precipitated zirconia and alumina with 2%
deposited alumina (Comparative Example 3B).
TABLE-US-00003 TABLE 3 Pigment Zirconia Content and Photocatalytic
Activity Value Co-precipitated HSPCA Pigment Sample Zirconia
content (wt. %) slope Example 3 0.20 1.4 Comparative Example 3A
0.20 2.1 Comparative Example 3B none 2.5
[0080] Example 3 illustrates the novel process of the instant
invention, wherein titanium dioxide pigment is produced having
deposited thereon in two sequential steps, an inorganic oxide wet
treatment comprising 3.0% dense silica, followed by a mixed
inorganic oxide wet treatment comprising 2.0% alumina
co-precipitated with 0.2% zirconia (percents are by weight of the
pigment). The substantial durability performance increase
(decreased HSPCA value versus comparative example) of the inventive
pigment indicates uniform incorporation of the co-precipitated
zirconia into the alumina treatment. The resulting titanium dioxide
pigment is particularly useful in the production of end-use
articles and compositions including plastics and coatings,
especially for exterior applications.
Example 4
[0081] Particulate titanium dioxide pigment intermediate obtained
from the vapor phase oxidation of titanium tetrachloride and
containing 0.6% alumina in its crystalline lattice was dispersed in
water in the presence of 0.18% by weight (based on pigment) of
sodium hexametaphosphate dispersant, along with a sufficient amount
of sodium hydroxide to adjust the pH of the dispersion to a minimum
value of 9.5, to achieve an aqueous dispersion with a solids
content of 35% by weight. The resulting titanium dioxide slurry was
sand milled, using a zircon sand-to-pigment weight ratio of 4 to 1,
until a volume average particle size was achieved wherein more than
90% of the particles were smaller than 0.63 microns, as determined
utilizing a Microtrac X100 Particle Size Analyzer.
[0082] The resulting slurry, diluted to 30% solids by weight, was
heated to 70.degree. C. and acidified to pH of about 6.0 using 36%
by weight sulfuric acid solution. Following a digestion period of
15 minutes at a pH of 6, 3.0% alumina, by weight of final pigment,
was added over 20 minutes as a 180 gram/liter aqueous sodium
aluminate solution, while maintaining the pH of the slurry at a
value of 6 via the concomitant addition of 36% aqueous sulfuric
acid solution, said sulfuric acid solution containing zirconium
oxychloride dissolved therein at a concentration calculated to
achieve 0.2%, by weight based on titanium dioxide, of
co-precipitated zirconium oxide.
[0083] The dispersion was allowed to equilibrate at 70.degree. C.
for 15 minutes, at which point the pH of the slurry was re-adjusted
to 7.0, prior to filtration while hot. The resulting filter cake
was washed with an amount of water, which had been preheated to
60.degree. C. and pre-adjusted to a pH of 7.0, equal to 1.5 times
the estimated weight of recovered pigment.
[0084] The washed semi-solid filter cake was subsequently
re-dispersed in water with agitation, and dried using an APV Nordic
PSD52 Spray Dryer, maintaining a dryer inlet temperature of
approximately 280.degree. C., to yield a dry pigment powder. The
dry pigment powder was then steam micronized in the presence of
0.35% by weight based on pigment of trimethylol propane, utilizing
a steam to pigment weight ratio of 2.5, with a steam injector
pressure set at 146 psi and micronizer ring pressure set at 118
psi, completing the finished pigment preparation.
[0085] The resulting pigment produced according to the inventive
process was tested for zirconia content and photocatalytic activity
as described in Example 1. Results are provided in Table 4,
together with comparative results from two finished pigment
samples; the first prepared utilizing the same procedure described
above, except that the zirconium oxychloride reagent was
batch-added immediately before the addition of the sodium aluminate
solution (Comparative Example 4A), and the second prepared
utilizing the same procedure described above, but in the absence of
the addition of zirconium oxychloride to the sulfuric acid solution
used during the alumina deposition step, thus replacing the mixed
oxide treatment of co-precipitated zirconia and alumina with 3%
deposited alumina (Comparative Example 4B).
TABLE-US-00004 TABLE 4 Pigment Zirconia Content and Photocatalytic
Activity Value Co-precipitated Zirconia HSPCA Pigment Sample
content (wt. %) slope Example 4 0.20 13 Comparative Example 4A 0.20
14 Comparative Example 4B none 18
[0086] Example 4 illustrates the novel process of the instant
invention, wherein titanium dioxide. pigment is produced having
deposited thereon in a single step, a mixed inorganic oxide wet
treatment comprising 3.0% alumina co-precipitated with 0.2%
zirconia (percents are by weight of the pigment). The durability
performance increase (decreased HSPCA value versus comparative
example) of the inventive pigment indicates uniform incorporation
of the co-precipitated zirconia into the alumina treatment. The
resulting titanium dioxide pigment is particularly useful in the
production of architectural and industrial coatings.
Example 5
[0087] Particulate titanium dioxide pigment intermediate obtained
from the vapor phase oxidation of titanium tetrachloride containing
1.0% alumina was dispersed in water in the presence of 0.15% by
weight (based on pigment) of sodium hexametaphosphate dispersant,
along with a sufficient amount of sodium hydroxide to adjust the pH
of the dispersion to a value of 9.5 or greater, to achieve an
aqueous dispersion with a solids content of 35% by weight. The
resulting titanium dioxide slurry was sand milled, using a zircon
sand-to-pigment weight ratio of 4 to 1, until a volume average
particle size was achieved wherein more than 90% of the particles
were smaller than 0.63 microns, as determined utilizing a Microtrac
X100 Particle Size Analyzer.
[0088] The resulting slurry, diluted to 30% solids by weight, was
heated to 70.degree. C. and subsequently treated with 1.8%,
calculated as alumina by weight of final pigment, of sodium
aluminate, added over 20 minutes as a 180 gram/liter aqueous sodium
aluminate solution, and 5.0% by weight of trisodium phosphate,
added over ten minutes as a 10% solution in water. While
maintaining the temperature at 70.degree. C., the pH of the slurry
was slowly decreased to a pH of 7.0 over a 55 minute period via the
slow addition of 36% by weight aqueous sulfuric acid solution, said
sulfuric acid solution containing zirconium oxychloride dissolved
therein at a concentration calculated to achieve 0.2%, by weight
based on titanium dioxide, of co-precipitated zirconium oxide.
Following a digestion period of 15 minutes at a pH of 7, 3.2%
alumina, by weight of final pigment, was added over 30 minutes as a
180 gram/liter aqueous sodium aluminate solution, while maintaining
the pH of the slurry at value of 7 via the concomitant addition of
36% aqueous sulfuric acid solution, said sulfuric acid solution
containing no other dissolved ingredients.
[0089] The dispersion was allowed to equilibrate at 70.degree. C.
for 15 minutes, at which point the pH of the slurry was re-adjusted
to 7.0, prior to filtration while hot. The resulting filter cake
was washed with an amount of water, which had been preheated to
60.degree. C. and pre-adjusted to a pH of 7.0, equal to 1.5 times
the estimated weight of recovered pigment.
[0090] The washed semi-solid filter cake was subsequently
re-dispersed in water with agitation, and dried using an APV Nordic
PSD52 Spray Dryer, maintaining a dryer inlet temperature of
approximately 280.degree. C., to yield a dry pigment powder. The
dry pigment powder was then steam micronized in the presence of
0.35% by weight based on pigment of trimethylol propane, utilizing
a steam to pigment weight ratio of 2.5, with a steam injector
pressure set at 146 psi and micronizer ring pressure set at 118
psi, completing the finished pigment preparation.
[0091] The resulting pigment produced according to the inventive
process was tested for zirconia content and photocatalytic activity
as described in Example 1. Results are provided in Table 5,
together with comparative results from two finished pigment
samples; the first prepared utilizing the same procedure described
above except that the zirconium oxychloride reagent was batch-added
immediately following the addition of the trisodium phosphate
solution (Comparative Example 5A), and the second prepared
utilizing the same procedure described above, but in the absence of
the addition of the zirconium oxychloride to the sulfuric acid
solution used during the aluminum phosphate deposition step, thus
replacing the mixed phosphate-oxide treatment of co-precipitated
zirconia and aluminum phosphate with 3.8% deposited aluminum
phosphate (Comparative Example 5B).
TABLE-US-00005 TABLE 5 Pigment Zirconia Content and Photocatalytic
Activity Value Co-precipitated Zirconia HSPCA Pigment Sample
content (wt. %) slope Example 5 0.20 2.6 Comparative Example 5A
0.20 2.8 Comparative Example 5B none 3.9
[0092] Example 5 illustrates the novel process of the instant
invention, wherein titanium dioxide pigment is produced having
deposited thereon in two sequential steps, a mixed inorganic
phosphate-oxide wet treatment comprising 3.8% aluminum phosphate
co-precipitated with 0.2% zirconia, followed by 3.2% alumina
(percents are by weight of the pigment). The durability performance
increase (decreased HSPCA value versus comparative example) of the
inventive pigment indicates uniform incorporation of the
co-precipitated zirconia into the aluminum phosphate treatment. The
resulting titanium dioxide pigment is particularly useful in the
production of end-use articles and compositions including plastics,
coatings, and, in particular, paper laminates.
* * * * *